Neutral brown heat absorbing glass composition



3,296,004 NEUTRAL BROWN HEAT ABSORBING GLASS COMPOSITION James E. Duncan, Natrona Heights, Pa., assignor to Pittsburgh Plate Glass Company, Pittsburgh, Pa., a

corporation of Pennsylvania N Drawing. Filed Aug. 12, 1963, Ser. No. 301,669

Claims. (Cl. 10652) The present invention relates to a neutral brown (bronze) colored, heat absorbing glass, and it has particular relation to a neutral brown (bronze) colored, heat absorbing sheet or plate glass having controlled energy and light transmittance characteristics.

Architects and building owners have shown an increasing interest in glazing windows in buildings with a neutral warm brown or bronze colored glass. This type of glass is desired to reduce glare and to provide a pleasing color in combination with intertior decorations. It is also desired that the glass absorb a substantial portion of the heat from the suns rays. This reduces the load on air conditioning systems employed to control the temperature of the interior of the building and permits the use of smaller and less costly systems.

In order for a glazing glass to qualify as a heat absorbing glass, it must have a total solar energy transmittance of less than 50 percent at one-quarter inch thickness. This standard has been established by Federal specification DDG-45 1A. The conventional type of heat absorbing glass has a bluish-green color imparted to it by the incorporation of controlled amounts of iron oxide in the glass. The bluish-green color of this type of glass is objected to by architects and building owners for aesthetic reasons. It is therefore an object of the present invention to provide a pleasing brown colored, heat absorbing glass which is suitable for glazing windows in building structures.

The development of a neutral brown glass having a pleasing color has required a careful consideration of the transmittance characteristics of the glass. The luminous transmittance must be limited in order to provide the desired protection from glare or excessive brightness. Glasses are available which have proper heat absorptive properties but which have undesirably low luminous transmittance. If the luminous transmittance is limited to too great an extent, the glass presents a degree of dreariness or depression on dark days.

The present invention contemplates a neutral brown, heat absorbing glass having a luminous transmittance of between 48 and 56 percent, usually between 49 and 55 percent and preferably about 51 to 54 percent at onequarter inch thickness. This is a radical departure from glasses presently known and used in buildings.

The luminous transmittance is the summation of the percentage of the incident, visible radiant energy (weighted by the energy distribution of the source and the eyes sensitivity) that will pass through the glass as described. In the present invention the source, unless otherwise stated, is Illuminant C, a standard source adopted by the International Commission on Illumination.

It is desired that the glass approach neutrality of color for aesthetic reasons. A neutral colored glass with a warm brown tint has been found to provide a most pleasing colored glass. A sheet of the glass one-quarter inch in thickness should have substantially uniform transmittance of light in the portion of the spectrum lying between 400 and 750 millimicrons; an excitation purity of between 6.0 and 12 percent and usually between 7 and 10.5 percent; a dominant wavelength of between 57 8 and 582 millimicrons and usually about 580 millimicrons; and a total solar energy transmission of less than 50 percent and usually between 45 and 49.8 percent.

CROSS REFERENCE ice The specifications for determining color, such as the dominant wavelength and excitation purity, have been derived from tristimulus values that have been adopted by the International Commission on Illumination as a direct result of experiments involving many observers. These specifications can be determined by calculating the trichromatic coefiicients, X, Y and Z, from the tristimulus values. The trichromatic coefficient, X and Y, are plotted on a chromaticity diagram and compared with the coordinates of Illuminant C as a standard light source. This comparison provides the information to determine the excitation purity and dominant wavelength. The lower the excitation purity of a color, the closer it is to being a neutral color. An understanding of these terms and definitions thereof may be had by referring to the Handbook of Colorimetry prepared by the staff of the Color Measurement Laboratory, Massachusetts Institute of Technology, under the direction of Arthur C. Hardy. This book was printed in 1936 by the Technology Press, Massachusetts Institute of Technology, Cambridge, Massachusetts. The trichromatic coefiicient values for the neutral brown glass compositions of this invention range as follows:

Trlchromatie Permissive Range Usual Range Coetfieients 0.322 to 0.332; 0.324 to 0.330. 0.320 to 0.350 0.325 to 0.345. 0.358 to 0.318 0.351 to 0.325.

The trichromatic coefficient Z value is obtained by adding X and Y and subtracting the total from 1.0.

In accordance with the present invention, a glass having the desired color and transmittance properties is provided. Such a glass is substantially free of nickel and contains by Weight 60 to percent SiO 11 to 20 percent Na O, 0 to 10 percent K 0, the sum of Na O and K 0 being 11 to 21 percent, 6 to 16 percent C210, 0 to 10 percent MgO, the sum of CaO and MgO being 6 to 20 percent, 0.2 to 1 percent Fe O 0.001 to 0.02 percent C00, 0.0002 to 0.02 percent Se, 0 to 5.0 percent A1 0 0 to 1.0 percent CI and 0 to 1.0 percent S0 Preferred ranges of compositions that are illustrative of the invention are as follows:

Components Weight Percent s10. 65 to 74 68 to 72. NazO 11 to 1s 11 to 14. K10 0 to s 0 to 1. Naqo plus K10 11 to 16 11 to 15. 000.. 61:0 fito 13. MgO 11:06 1.5 to 4. 09.0 plus MgO 10 to 16 10 to 15. FenO; 0.2 to 0. 0.2 to 0.5. oo0 0.002 to 0.002 to 0.005. Se 0.001 to 0.001 to 0.01. A1101 0 to 5.0 0 to 5.0. CI 0 to 0 5 0 to 0.5. $0.. 0 to n 0 0 to 0.6.

SiO is the glass former. Sodium oxide is present as a flux to reduce the melting temperature of the glass. Po-

tassium oxide may be employed in place of a portion of the Na O, but the use of Na O is preferred because it is less expensive. The total amount of alkali metal oxide in the glass should range from 11 to 21 percent by weight. CaO and MgO are also employed as fluxes. They are used to supplement the Na O because they improve the chemical durability of the glass. The amount of alkaline earth metal oxides in the glass can range from 6 to 20 percent by weight.

Alumina may be present in the glass in varying amounts, depending mainly upon the manner in which the glass is formed. Alumina is employed to regulate the viscosity of SEARCH R0004 the glass, improve its durability and prevent devitrifica'tion of the glass. Relatively small amounts of alumina, for example, less than 1.0 percent by weight, are employed when plate glass is cast from a pot or made in a tank and formed by rolling it horizontally between sizing rolls. However, when the glass is formed by drawing it vertically from the kiln of a tank over a draw bar and upwardly between rollers (sheet glass), up to' percent By weight alumina can be employed. Usually, however from 1.0 to 3.5 percent by weight alumina is employed when forming glass by the sheet or vertical drawing prcicedufe.

Trace amounts of TiO are frequently present, e.'g.-, in amounts up to 0.05 percent byweight, as an impurity.-

Fe O is employed principally to provide the desired heat absorbingproperties to the glass. C00 and Se are present in combination with Fe O to provide the desired luminous and total energy transmittance and color to the glass. With th proper combination of the three colorants it has Been discovered that a pleasing neutral brown or bronze 6010; can be pi odu'ced. Such glass does not have an undesirable greenish brown cast but instead possesses the warmth of a neutral brown glass combined with a high luminous transmittance in the visible range and suflicient Heat absorptive properties to make it unusually attractive frlglaz'ing windows in the buildings.

The glasses of the invention can be produced from convefitional glass making materials properly compounded andthor'oughly mixed so as to yield, when reacted, glasses of the desired ultimate composition. Suitable batch materials include 'sand, soda ash, potassium carbonate, limestone, dolomite, aluminum hydrate, salt cake, common salt,- sodium nitrate, arsenious oxide, antimony oxide, aplit, feldspar, rouge cobalt oxide and selenium metal. The salt cake,- common salt, sodium nitrate, antimony oxide, arsefiious oxide and combinations thereof may be present in the batch to act as refining agents.

Various size pots or crucibles can be employed and the melting temperatures and times will vary according to the amount being formed. Also, the glass can be formed continuously in the form of a sheet when made in a tank.

EXAMFLE I Weight parts Batch ingredient: (for batch) Sand pounds 1000 Soda ash do 277 Limestone do 217 Dolomite do 149 Sodium nitrate do 30 Common salt do 25 Salt cake do Rouge (98 percent Fe O d-o 6.25 Cobalt oxide ounces 0.75 Selenium do 1.75

A laboratory pot glass batch, which is illustrative of the present invention, is prepared by thoroughly mixing one-twentieth weight fraction of the above batch ingredients (5 percent). This smaller pot batch yields approximately 70 pounds of glass after melting and fining which is conducted as follows:

An empty refractory clay pot is preheated in the furnace at a furnace temperature of about 2100 F., the furnace being heated by the controlled combustion of natural gas. A portion (approximately of the mixed batch is ladled into the preheated pot and the furnace temperature is gradually increased. The remaining portion of the mixed batch is ladled into the pot over a period of 2 hours, and the temperature is raised gradually to about 2650 F. during this time. The temperature is maintained at 2650 F. for the next 3% hours to refine the glass. At the end of this time, the chemical reactions are completed; the glass is free of bubbles and is substantially homogeneous.

In the preparation of the glasses of the present invie'nti on neutral to oxidizing conditions are observed in the melting 'and fi ming furnace.

After the glass is refined, the temperature of the furnace is reduced to 2100" F. over a period of hour. The funrace is then held at this temperature for /2 hour. The pot is removed from the furnace and the glass is poured on a metal table and rolled in the form of a plate. The plate is placed in a kiln and cooled from 1150 to 800 F. ata rate of about 7 F. per minute. Thereafter the glass is cooled more rapidly to room temperature and subsequently cut into pieces suitable for grinding, polishing and testing.

The calculated composition of the above given batch is as follows.

Calculated Component: percent by W. SiO 70.9

- CaO -5. 11.7 MgO 2.3 80;. 0.4

Fe O 0.5

A chemical analysis of a sample of the glass made in a clay pot yields the following composition:

Wet chemical analysis analysis is not surprising since selenium is volatile and a good portion thereof is lost in melting and fining.

This factor coupled with the reasonable realm of experimental error involved in the absorption spectrophotometric analysis for selenium (a diflicult metal to analyze) accounts for the difference in selenium content between the calculated composition and the analysis.

A one-quarter inch thick sample of a glass made by the pot method when subjected to optical and spectral transmittance measurements yields the following values:

Property:

Luminous transmittance (illuminant C) percent 53.5 Total solar energy transmittance do 49.4 Excitation purity do 9.0 Dominant wavelength millimicrons 579 Trichromatic coeflicients (plus or minus X .3276 Y .3314 Z .3410

A typical batch formula which was used when this glass was made in a tank and formed as a continuous ribbon was as follows.

Representative samples of glass taken during various stages of a given production campaign were subjected to chemical analyses, yielding the following results:

WET CHEMICAL ANALYSIS Sample 1 Sample 2 Sample 3 (percent) (percent) (percent) ABSORPTION SPECTROPHOTOMET RIC ANALYSIS Total 99. 99 99. 99 100. 0

Typical transmittance data at the various wavelengths indicated hereinbelow for 0.250 inch thick test representative samples of glass plates formed at a given stage in a continuous production campaign by the tank method marked A and by pot method marged B are tabulated below.

Percent Transmittance Wavelength (millimicrons) Glasses within the purview of the present invention can have transmittance values in the visible portion of the spectrum which may vary about 8 percent in transmittance above or 8 percent in transmittance below the transmittance values given above at a particular wavelength.

The spectral transmittance measurements of the glasses of the present invention are made by standard spectrophotometric methods utilizing three different spectrophotometers. A Bechrnan Quartz Spectrophotometer, Model DU is used for wavelengths between 300 and 400 millimicrons and between 750 and 1000 millimicrons. A General Electric Recording Spectrophotometer, Model No. 596200563 is used for the visible range of the spectrum, 400 to 750 millimicrons. A Perkin-Elmer Spectrophotometer, Model 12 having a NaCl prism is used for wavelengths above 1000 millimicrons.

The batch formulas, calculated compositions and chemical analyses set forth herein represent preferred compositions for nominal inch thicknesses, viz. 0.250 inch thick plus or minus about 0.030 inch. The amounts of the colorants, F6203, C00 and Se, must be carefully controlled to achieve the desired color, transmittance and heat-absorbing characteristics at various thicknesses. Exemplary weight ranges for the colorants for inch thick glass are 0.3 to 0.5 percent Fe O 0.002 to 0.005 percent C00 and 0.001 to 0.003 percent Se. When the glasses are fabricated at greater or lesser thicknesses than A inch, it is necessary to decrease or increase, respectively, the amounts of each colorant to obtain the requisite color, transmittance and heat-absorbing characteristics. For example, when the glass is produced in /8 inch thickness, the amount of each of the colorants can be approximately doubled to achieve the same color, heat absorption and transmittance characteristics.

If too much Fe O is employed to make a glass of a given thickness, the color is more green than desired and the luminous transmittance will be reduced. If too little Fe O is used, the heat absorption properties of the glass are diminished. If too much selenium is present, the color of the glass is more red than desired; and if too little selenium is present, the color is more bluish green than desired. It the glass contains too much CoO, its color is more blue than desired; whereas, if the glass does not contain enough C00, its color is more greenish brown than is desired. Although NiO usually provides a reddish brown color to lime-soda-silica glasses, its presence is not desirable in any appreciable amount in the glasses of the invention for it tends to lower the luminous transmittance too much when combined with the above described amounts of Fe O Se and C00 which are employed to obtain high solar energy absorption, relatively high luminous transmittance for a heat absorbing glass and the warm brown color.

As mentioned hereinabove, the glasses of this invention are heat absorbing and provide a high measure of solar heat control. Typical solar transmittance data for nominal 0.250 inch thick (plus or minus 0.001 inch) representative glass plates produced by the tank method during the campaign referred to above in Example 2 is as follows:

portion of the spectrum lying between 400 and 75 millimicrons, a dominant wavelength of between about 57 8 1 The models the value which occurs most frequently. 2 The typical is one particular sample representing accumulated data.

The total solar energy transmittance values as reported herein are calculated from the spectral transmittance of the glass and'the spectral distribution of solar radiant energy. The latter values are those of Parry Moon (Journal of the Franklin Institute, vol 230, November 1940).

The glass as thus produced represents a fresh ap- 2 proach; a change in the appearance of glazing glasses. It provides architects with complete aireedom from color problems in daylight for interior planning. The careful selection of colorants permits the production of a glass having excellent brightness or glare control. It also permits the production of a glass having a high order of solar heat absorption with a pleasing neutral brown color. These properties can be readily reproduced in successive melts of the glass.

The glasses of this invention can be employed in laminates; windows; television implosion panels, tempered tor untempered, curved or flat; sliding glass doors; glass curtain walls; glass facades tor buildings and insulating glass structures, e.-g. those having a plurality of layers of glass mounted in a common frame and having air as an insulation medium between the plates.

Although the present invention has been described with reference to specific details of certain embodiments, it is not intended that such details act as limitations upon the scope of the invention except insofar as included in the accompanying claims.

I claim:

1. A neutral brown colored, heat absorbing glass having substantially uniform transmittance of light in the portion of the spectrum lying between 400 and 750 millimicrons and an excitation purity between 6 and :12 percent, consisting essentially of the following ingredients in percent by weight: 60 to 75 percent SiO 11 to 9.0 percent Na O, 0 to 10 percent \K -O, the sum of N370 and K 0 being 11 to 21 percent, 6 to 16 percent Cal), 0 to 10 percent MgO, the sum of CaO and MgO being 6 to 20 percent, 0.2 to 1 percent Fe O 0.001 to 0.02 percent 000 and 0.0005 to 0.02 percent Se, the amounts of Se, C00 and Fe O being coordinated to produce a neutral brown glass having said transmittance propert-it s.

2. A glass according to claim 1 containing up to percent by weight A1 0 3. A neutral brown colored, heat absorbing glass ha 7- ing substantially uniform transmittance of light in the portion of the spectrum lying between 400 and 750 millimicrons, a dominant wavelength of between 578 and 582 millimicrons, and an excitation purity between 6 and 12 percent, consisting essentially of the following ingredients in percent by weight: 65 to 74 percent SiO 11 to 15 percent Na O, 0 to 5 percent K 0, the sum of Na O and K 0 being 11 to 16 percent, '6 to 15 percent CaO, l to 6 percent MgO, the sum of CaO and MgO being to 16 percent, 0.2 to 0.8 percent Fe O 0.002 to 0.01 percent CoO and 0.0011 to 0.015 percent Se, the amounts of Se, C00 and Fe O being coordinated to produce a neutral brown glass having said transmittance properties.

4. A glass according to claim 3 containing up to 5 percent by weight A1 0 5. A neutral brown colored, heat absorbing glass having substantially uniform transmittance of light in the and about 582 millimicrons, and an excitation purity between about 6 and about 9.5 percent, consisting essen-- tially of the following ingredients in percent by weight:

68 to 72 percent SiO 11 to 14 percent Na O, 0 to 1.

percent K 0, the sum of Na O and K 0 being 11 to 15 percent, 6 to 13 percent CaO, 1.5 to 4 percent MgO, the:

0 sum of CaO and MgO being 10 to 15 percent, 0.2 to 05 percent Fe O 0.002 to 0.005 percent 000 and 0.001 to 0.01 percent Se, the amounts of Se, C00 and f e- 0 be-- ing coordinated to produce a neutral brown glass having said transmittance properties.

6. A glass according to claim 5 containing up to 5' percent by weight A1 0 7. An article of manufacture comprising a neutral brown colored, heat absorbing plate of glass at a thickness suitable for glazing so as to have substantially uniform transmission of light in the portion of the spectrum lying between 400 and 750 millimicrons, an excitation purity between 6 and 12 percent and a total luminous transmittance between 48 and '56 percent, consisting esscntially of the following ingredients in percent by weight: 60 to 75 percent Si'O 11 to 20 percent Na O, 0 to 10 percent K 0, the sum of Na O and K 0 being 11 to 21 percent, 6 to 16 percent CaO, 0 to 10 percent MgO, the sum of CaO and MgO being 6 to 20 percent, 0.2 to 1 percent Fe O 0.001 to 0.02 percent 000 and 0.0005 to 0.02 percent Se, the amounts of Se, C00 and Fe O being coordinated to produce a neutral brown glass having said transmittance properties.

8. An article of manufacture as in claim 7 wherein said glass contains up to 5 percent A1 0 9. An article of manufacture comprising :a neutral brown colored, heat absorbing plate of glass approximately one-eighth to approximately one-quarter inch in thickness suitable {for glazing purposes and having substantially uniform transmission of light in the portion of the spectrum lying between 400 and 750 millimicrons, an exitation purity of between 6 and 12 percent and a total luminous transmittance between 48 and 56 percent, the glass consisting essentially of the 'iollowing ingredients in percent by weight: 60 to 75 percent SiO 11 to 20 percent Na O, 0 to 10 percent K 0, the sum of Na O and K 0 being 111 to 21 percent, 6 to 16 percent CaO, 0 to 10 percent MgO, the sum of CaO and MgO being 6 to 20 percent, together with 0.3 to 0.5 percent Fe O 0.002 to 0.005 percent C00 and 0.001 to 0.003 percent So at one-quarter inch thickness, the amount of the colorants Fe o C00 and Se being greater as the thickness of the sheet is less than one-quarter inch and being approximately twice the above listed amount for each colorant when the thickness of the plate is oneeighth inch.

10. A glass article as in claim 9 wherein said glass contains up to 5 percent A1 0 References Cited by the Examiner UNITED STATES PATENTS 2,902,377 9/ 1959 Duncan 10652 2,938,808 5/1960 Duncan et al. 106-52 TOBIAS E. LEVOW, Primary Examiner. H. MCCARTHY, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,296 ,004 January 3 1967 James E. Duncan It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7, line 47, beginning with "in percent" strike out all to and including propertiesHn line 55 same column 7 and insert instead the following:

in percent by weight: 60 to 75 percent Si0 11 to 20 percent NazO 0 to 10 percent K 0 the sum of Na O and K 0 being 11 to 21 percent, 6 to 16 percent Ca0, 0 to 10 percent MgO, the sum of CaO and MgO being 6 to 20 percent 0 2 to 1 percent Fe 0 0.001 to 0.02 percent C00 and 0 .0005 to 0.02 percent See, the amounts of Se, C00 and FezO being coordinated to produce a neutral brown glass having said transmittance properties.

Signed and sealed this 13th day of August 1968.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

Attesting Officer EDWARD BRENNER Commissioner of Pat 

1. A NEUTRAL BROWN COLORED, HEAT ABSORBING GLASS HAVING SUBSTANTIALLY UNIFORM TRANSMITTANCE OF LIGHT IN THE PORTION OF THE SPECTRUM LYING BETWEEN 400 AND 750 MILLIMICRONS AND AN EXCITATION PURITY BETWEEN 6 AND 12 PERCENT, CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS IN PERCENT BY WEIGHT; 60 TO 75 PERCENT SIO2, 11 TO 20 PERCENT NA2O, 0 TO 10 PERCENT KA2O, THE SUM OF MA2O AND K2O BEING 11 TO 21 PERCENT, 6 TO 16 PERCENT CAO, 0 TO 10 PERCENT MGO, THE SUM OF CAO AND MGO BEING 6 TO 20 PERCENT, 0.2 TO 1 PERCENT FE2O3, 0.001 TO 0.02 PERCENT COO AND 0.0005 TO 0.02 PERCENT SE. THE AMOUNTS OF SE, COO AND FE2O3 BEING COORDINATED TO PRODUCE A NEUTRAL BROWN GLASS HAVING SAID TRANSMITTANCE PROPERTIES. 